Correlated plasma wave, magnetic field, and energetic ion observations in the ion pickup region of comet Giacobini‐Zinner

Abstract

Relationships between simultaneous plasma wave, magnetic field, and energetic heavy ion data obtained by the International Cometary Explorer (ICE) spacecraft in the large‐scale solar wind particle pickup region surrounding comet Giacobini‐Zinner are examined. In particular, we investigate the conditions under which electrostatic emissions at frequencies of a few kilohertz and electromagnetic waves at a few tens of hertz are observed. It is shown that the data are consistent with the view that the kilohertz electrostatic emissions result from a beam‐type instability excited by the pickup photoelectron population when the angle α between the magnetic field and the plasma velocity vectors is not too large (α < 60°). The data also suggest that the few tens of hertz electromagnetic waves may be excited by a ring‐type instability associated with the pickup ion population, which occurs when the magnetic field is near to orthogonality with the flow (α > 60°).